/**
 * http://surenpi.com
 */
package org.suren.autotest.web.framework.util;

import java.io.IOException;
import java.io.OutputStream;

/**
 * @author suren
 * @date 2016年8月4日 下午12:30:41
 */
public class LZWEncoder
{
	private static final int	EOF			= -1;
	private int					imgW, imgH;
	private byte[]				pixAry;
	private int					initCodeSize;
	private int					remaining;
	private int					curPixel;
	// GIFCOMPR.C - GIF Image compression routines
	//
	// Lempel-Ziv compression based on 'compress'. GIF modifications by
	// David Rowley (mgardi@watdcsu.waterloo.edu)
	// General DEFINEs
	static final int			BITS		= 12;
	static final int			HSIZE		= 5003;			// 80% occupancy
	// GIF Image compression - modified 'compress'
	//
	// Based on: compress.c - File compression ala IEEE Computer, June 1984.
	//
	// By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
	// Jim McKie (decvax!mcvax!jim)
	// Steve Davies (decvax!vax135!petsd!peora!srd)
	// Ken Turkowski (decvax!decwrl!turtlevax!ken)
	// James A. Woods (decvax!ihnp4!ames!jaw)
	// Joe Orost (decvax!vax135!petsd!joe)
	int							n_bits;						// number of
																// bits/code
	int							maxbits		= BITS;			// user settable
																// max #
																// bits/code
	int							maxcode;						// maximum code,
																// given n_bits
	int							maxmaxcode	= 1 << BITS;		// should NEVER
																// generate this
																// code
	int[]						htab		= new int[HSIZE];
	int[]						codetab		= new int[HSIZE];
	int							hsize		= HSIZE;			// for dynamic
																// table sizing
	int							free_ent	= 0;				// first unused
																// entry
	// block compression parameters -- after all codes are used up,
	// and compression rate changes, start over.
	boolean						clear_flg	= false;
	// Algorithm: use open addressing double hashing (no chaining) on the
	// prefix code / next character combination. We do a variant of Knuth's
	// algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
	// secondary probe. Here, the modular division first probe is gives way
	// to a faster exclusive-or manipulation. Also do block compression with
	// an adaptive reset, whereby the code table is cleared when the compression
	// ratio decreases, but after the table fills. The variable-length output
	// codes are re-sized at this point, and a special CLEAR code is generated
	// for the decompressor. Late addition: construct the table according to
	// file size for noticeable speed improvement on small files. Please direct
	// questions about this implementation to ames!jaw.
	int							g_init_bits;
	int							ClearCode;
	int							EOFCode;
	// output
	//
	// Output the given code.
	// Inputs:
	// code: A n_bits-bit integer. If == -1, then EOF. This assumes
	// that n_bits =< wordsize - 1.
	// Outputs:
	// Outputs code to the file.
	// Assumptions:
	// Chars are 8 bits long.
	// Algorithm:
	// Maintain a BITS character long buffer (so that 8 codes will
	// fit in it exactly). Use the VAX insv instruction to insert each
	// code in turn. When the buffer fills up empty it and start over.
	int							cur_accum	= 0;
	int							cur_bits	= 0;
	int							masks[]		=
											{ 0x0000, 0x0001, 0x0003, 0x0007,
			0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF,
			0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF };
	// Number of characters so far in this 'packet'
	int							a_count;
	// Define the storage for the packet accumulator
	byte[]						accum		= new byte[256];

	// ----------------------------------------------------------------------------
	LZWEncoder(int width, int height, byte[] pixels, int color_depth)
	{
		imgW = width;
		imgH = height;
		pixAry = pixels;
		initCodeSize = Math.max(2, color_depth);
	}

	// Add a character to the end of the current packet, and if it is 254
	// characters, flush the packet to disk.
	void char_out(byte c, OutputStream outs) throws IOException
	{
		accum[a_count++] = c;
		if (a_count >= 254)
			flush_char(outs);
	}

	// Clear out the hash table
	// table clear for block compress
	void cl_block(OutputStream outs) throws IOException
	{
		cl_hash(hsize);
		free_ent = ClearCode + 2;
		clear_flg = true;
		output(ClearCode, outs);
	}

	// reset code table
	void cl_hash(int hsize)
	{
		for (int i = 0; i < hsize; ++i)
			htab[i] = -1;
	}

	void compress(int init_bits, OutputStream outs) throws IOException
	{
		int fcode;
		int i /* = 0 */;
		int c;
		int ent;
		int disp;
		int hsize_reg;
		int hshift;
		// Set up the globals: g_init_bits - initial number of bits
		g_init_bits = init_bits;
		// Set up the necessary values
		clear_flg = false;
		n_bits = g_init_bits;
		maxcode = MAXCODE(n_bits);
		ClearCode = 1 << (init_bits - 1);
		EOFCode = ClearCode + 1;
		free_ent = ClearCode + 2;
		a_count = 0; // clear packet
		ent = nextPixel();
		hshift = 0;
		for (fcode = hsize; fcode < 65536; fcode *= 2)
			++hshift;
		hshift = 8 - hshift; // set hash code range bound
		hsize_reg = hsize;
		cl_hash(hsize_reg); // clear hash table
		output(ClearCode, outs);
		outer_loop: while ((c = nextPixel()) != EOF)
		{
			fcode = (c << maxbits) + ent;
			i = (c << hshift) ^ ent; // xor hashing
			if (htab[i] == fcode)
			{
				ent = codetab[i];
				continue;
			}
			else if (htab[i] >= 0) // non-empty slot
			{
				disp = hsize_reg - i; // secondary hash (after G. Knott)
				if (i == 0)
					disp = 1;
				do
				{
					if ((i -= disp) < 0)
						i += hsize_reg;
					if (htab[i] == fcode)
					{
						ent = codetab[i];
						continue outer_loop;
					}
				} while (htab[i] >= 0);
			}
			output(ent, outs);
			ent = c;
			if (free_ent < maxmaxcode)
			{
				codetab[i] = free_ent++; // code -> hashtable
				htab[i] = fcode;
			}
			else
				cl_block(outs);
		}
		// Put out the final code.
		output(ent, outs);
		output(EOFCode, outs);
	}

	// ----------------------------------------------------------------------------
	void encode(OutputStream os) throws IOException
	{
		os.write(initCodeSize); // write "initial code size" byte
		remaining = imgW * imgH; // reset navigation variables
		curPixel = 0;
		compress(initCodeSize + 1, os); // compress and write the pixel data
		os.write(0); // write block terminator
	}

	// Flush the packet to disk, and reset the accumulator
	void flush_char(OutputStream outs) throws IOException
	{
		if (a_count > 0)
		{
			outs.write(a_count);
			outs.write(accum, 0, a_count);
			a_count = 0;
		}
	}

	final int MAXCODE(int n_bits)
	{
		return (1 << n_bits) - 1;
	}

	// ----------------------------------------------------------------------------
	// Return the next pixel from the image
	// ----------------------------------------------------------------------------
	private int nextPixel()
	{
		if (remaining == 0)
			return EOF;
		--remaining;
		byte pix = pixAry[curPixel++];
		return pix & 0xff;
	}

	void output(int code, OutputStream outs) throws IOException
	{
		cur_accum &= masks[cur_bits];
		if (cur_bits > 0)
			cur_accum |= (code << cur_bits);
		else
			cur_accum = code;
		cur_bits += n_bits;
		while (cur_bits >= 8)
		{
			char_out((byte) (cur_accum & 0xff), outs);
			cur_accum >>= 8;
			cur_bits -= 8;
		}
		// If the next entry is going to be too big for the code size,
		// then increase it, if possible.
		if (free_ent > maxcode || clear_flg)
		{
			if (clear_flg)
			{
				maxcode = MAXCODE(n_bits = g_init_bits);
				clear_flg = false;
			}
			else
			{
				++n_bits;
				if (n_bits == maxbits)
					maxcode = maxmaxcode;
				else
					maxcode = MAXCODE(n_bits);
			}
		}
		if (code == EOFCode)
		{
			// At EOF, write the rest of the buffer.
			while (cur_bits > 0)
			{
				char_out((byte) (cur_accum & 0xff), outs);
				cur_accum >>= 8;
				cur_bits -= 8;
			}
			flush_char(outs);
		}
	}
}
